ah we disagree then. this debate is not really 'provable' but it makes one wonder.
how much of that 300lbs was fat. a lot of it. I can go and grab a random obese guy off the street and he'll easily be stronger than a lot of trained lifters. there's one at my gym. just joined. never trained in his life. he reps out 285 for good reps on the flat.
does he have more lean tissue than a guy of his height who's 5-6% bf? no. he's fatter. there's a huge correlation between strength and sheer size.
he was a 14 year old with 300lb on him no shit he was fat. and no, there is no correlation between strength and fat tissue. zero. if you take a 450 pound man and liposuction 200 pounds of fat out of him he's not going to get weaker. that is 100%, categorically false what you said.
additionally, you're missing the goddamn point that just because there is a natural limit that doesn't mean it's even remotely within the grasp of 99% of people. my point was that, believe it or not, genetics DO play a role. that's why when you get two untrained individuals and put them in a gym they are not equally strong and do not have equal muscle tissue prior to lifting. it's why you get some guys who go from barely doing a pushup to benching 4 plates within a couple years and some guys never hit that mark.
your anecdote about the guy who just joined the gym proves my point. some guys spend ten years trying to get to the point of benching 3 plates and that guy just did it off the street. why? GENETICS. dude is just DNA encoded for muscle.
the whole "random obese guy" thing is just hogwash as well. it's not even slightly accurate. i can't count the number of obese people i've seen join gyms that struggle and wheeze with small weights. there's a huge lump of a man at an old gym i went to that trained his ass off for a few years and was only barely able to get 135 over his head for a few reps.
i don't know where you got your idea that all human beings are the exact same, but there isn't a lick of scientific evidence to support it.